Selina Solutions Concise Mathematics Class 6 Chapter 17 Idea of Speed, Distance and Time Exercise 17(A) help students get a clear idea of topics and the steps to be followed in solving problems with ease. The solutions prepared in an understandable language, by expert faculty at BYJU’S, help students to achieve high marks in the final examinations. Shortcut tips and formulas are covered in a stepwise manner, for a better understanding of the concepts. Selina Solutions Concise Mathematics Class 6 Chapter 17 Idea of Speed, Distance and Time Exercise 17(A) PDF, can be downloaded from the available links below.
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Exercise 17(A)
1. A train covers 51 km in 3 hours. Calculate its speed. How far does the train go in 30 minutes?
Solution:
Given
A train covers 51 km in 3 hours
So, distance = 51 km
Time = 3 hours
Hence,
Speed = 51 km/ 3 hours
We get,
= 17 km/h
Now for 30 minutes
Speed = 17 km/h
Time = 0.5 hours
Hence,
Distance = 17 × 0.5
We get,
= 8.5 km
Therefore, train covered 8.5 km in 30 minutes
2. A motorist travelled the distance between two towns, which is 65 km, in 2 hours and 10 minutes. Find his speed in metre per minute.
Solution:
Given
A motorist travelled the distance 65 km in 2 hours and 10 minutes
So, distance = 65 km
Time = 2 hours 10 minutes
Hence,
Speed = 65 km / (2 hours + 10 minutes)
We know that,
1 km = 1000 m
1 hour = 60 min
= 65 (1000 m) / [2 (60 min) + 10 min]
= 65000 m/130 min
We get,
= 500 m/min
Therefore, the speed of a motorist in meter per minute is 500 m/min
3. A train travels 700 metres in 35 seconds. What is its speed in km/h?
Solution:
Given
A train travels 700 metres in 35 seconds
So, distance = 700 m
Time = 35 sec
Hence,
Speed = 700 m / 35 sec
1000 m = 1 km
1 m = 0.001 km
700 m = 0.001 × 700
= 0.7 km
3600 seconds = 1 hour
1 sec = 1 / 3600 hour
35 sec = 35 / 3600
Now,
Speed = Distance / Time
= [0.7 / (35/ 3600)]
We get,
= (0.7 × 3600) / 35
= 2520 / 35
= 72 km/h
Therefore, the speed of train is 72 km/h
4. A racing car covered 600 km in 3 hours 20 minutes. Find its speed in metre per second. How much distance will the car cover in 50 sec?
Solution:
Given
A racing car covered 600 km in 3 hours and 20 minutes
So, distance = 600 km
Time = 3 hours 20 minutes
Hence,
Speed = 600 km / (3 hours + 20 minutes)
= 600 (1000m) / [3(60 min) + 20 min]
We get,
= 600000m / 200 min
= 600000m / 200 (60 sec)
We get,
= 600000 / 12000 sec
= 50 m / sec
Thus, speed in meter per second is 50 m / sec
Now, the distance covered by car in 50 sec is calculated as below
Speed = 50 m / sec
Time = 50 sec
Hence,
Distance = 50 × 50
= 2500 m
= 2.5 km
Therefore, the distance covered by car in 50 seconds is 2.5 km
5. Rohit goes 350 km in 5 hours. Find:
(i) his speed
(ii) the distance covered by Rohit in 6.2 hours
(iii) the time taken by him to cover 210 km
Solution:
(i) his speed
Given
Rohit goes 350 km in 5 hours
So, distance = 350 km
Time = 5 hours
Hence,
Speed = 350 km / 5 hours
We get,
= 70 km/h
Hence, Rohit speed is 70 km/h
(ii) the distance covered by Rohit in 6.2 hours
Given
Rohit goes 350 km in 5 hours
So, distance = 350 km
Time = 5 hours
Hence,
Speed = 350 km / 5 hours
We get,
= 70 km/h
Now, the distance covered by Rohit in 6.2 hours is calculated as below
Speed = 70 km/h
Time = 6.2 hours
Hence,
Distance = 70 × 6.2
= 434 km
Therefore, Rohit covers 434 km in 6.2 hours
(iii) the time taken by him to cover 210 km
Given
Rohit goes 350 km in 5 hours
So, distance = 350 km
Time = 5 hours
Hence,
Speed = 350 km / 5 hours
We get,
= 70 km/h
Now, the time taken by Rohit to cover 210 km is calculated as below
Distance = 210 km
Speed = 70 km/h
Hence,
Time = 210 km / 70 km/h
= 3 hours
Therefore, the time taken by Rohit to cover 210 km is 3 hours
6. A boy drives his scooter with a uniform speed of 45 km/h. Find:
(i) the distance covered by him in 1 hour 20 min
(ii) the time taken by him to cover 108 km
(iii) the time taken to cover 900 m
(i) the distance covered by him in 1 hour 20 min
Given
Speed of scooter is 45 km/h
Speed = 45 km/h
Time = 1 hours 20 minutes
Hence,
Distance = 45 × (1 + 20 / 60)
= 45 × (1 + 1 / 3)
We get,
= 45 × 4 / 3
= 15 × 4
= 60
Hence, the distance covered by a boy in 1 hour 20 minutes is 60 km
(ii) the time taken by him to cover 108 km
Given
Speed of scooter is 45 km/h
So, speed = 45 km/h
Distance = 108 km
Hence,
Time = 108 km / 45 km/h
We get,
= 12 / 5 h
=
h
This is equal to,
= 2 hours (2 / 5) × 60 min
= 2 hours (2 × 12) min
= 2 hours 24 min
Hence, the time taken by a boy to cover 108 km distance is 2 hours 24 min
(iii) the time taken to cover 900 m
Given
Speed of scooter is 45 km/h
So, speed = 45 km/h
Distance = 900 m
Hence,
Time = 900 m / 45 km/h
= (900 / 1000) × 1 / 45
We get,
= (9 / 10) × (1 / 45)
= 1 / 50 h
= (1 / 50) × 60 min
= 6 / 5 min
This can be written as,
= 1 and 1 / 5 min
= 1 min (1 / 5) × 60 sec
We get,
= 1 min 12 sec
Hence, the time taken by a boy to cover 900 m is 1 min 12 sec
7. I travel a distance of 10 km and come back in 2 ½ hours. What is my speed?
Solution:
Given
10 km distance travelled twice in 2 ½ hours
So, distance = 10 km + 10 km
= 20 km
Time = 2 ½ hours
This can be written as,
Time = 5 / 2 hours
Hence,
Speed = [20 km / (5 / 2 hours)]
= (20 × 2) / 5
We get,
= 40 / 5
= 8 km/h
Hence, the speed of a person to cover a distance of 10 km twice is 8 km/h
8. A man walks a distance of 5 km in 2 hours. Then he goes in a bus to a nearby town, which is 40 km, in further 2 hours. From there, he goes to his office in an autorickshaw, a distance of 5 km, in ½ hour. What was his average speed during the whole journey?
Solution:
Given
A man walks a distance of 5 km in 2 hours
40 km distance is covered by bus in 2 hours
5 km distance is covered by autorickshaw in ½ hour
Hence,
Total distance covered by a man during whole journey is calculated as below
Total distance = 5 km + 40 km + 5 km
= 50 km
Total time taken by a man during whole journey
Total time = 2 + 2 + 1/2
= (4 + 4 + 1) / 2
We get,
= 9 / 2 hours
Hence,
Average speed = 50 km / (9 / 2) hours
= (50 × 2) / 9 km/h
= 100 / 9 km/h
=Â 
km/h
Therefore, the average speed taken by a man during whole journey is 
km/h
9. Jagan went to another town such that he covered 240 km by a car going at 60 kmh-1. Then he covered 80 km by a train, going at 100 kmh-1 and the rest 200 km, he covered by a bus, going at 50 kmh-1. What was his average speed during the whole journey?
Solution:
Given
Jagan covered 240 km distance by a car at 60 km/h
He travelled 80 km distance by train at 100 km/h
He travelled 200 km distance by a bus at 50 km/h
Hence,
Total distance travelled by Jagan = 240 km + 80 km + 200 km
= 520 km
Now, total time taken by Jagan during whole journey is shown below
Time taken by car = 240 km / 60 km/h
= 4 hours
Time taken by a train = 80 km / 100 km/h
= 4 / 5 hours
Time taken by bus = 200 km / 50 km/h
= 4 hours
So, total time taken = 4 + 4 / 5 + 4
= (20 + 4 + 20) / 5
We get,
= 44 / 5 hours
Hence,
Average speed = total distance / total time
= 520 km / (44 / 5) hours
= [(520 × 5) / 44] km/h
= (130 × 5) / 11 km/h
= 650 / 11 km/h
=Â 
km/h
Hence, the average speed during the whole journey is 
km/h
10. The speed of sound in air is about 330 ms-1. Express this speed in kmh-1. How long will the sound take to travel 99 km?
Solution:
Given
Speed of sound in air = 330 m/sec
So, speed = 330 m/sec
Distance = 99 km
= 99 × 1000
We get,
= 99000 m
Hence,
Time = [(99000 m) / (330 m/sec)]
= 9900 / 33 sec
We get,
= 300 sec
= 5 min
Hence, the time taken by the sound to travel 99 km is 5 min
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